Neurodegenerative diseases are associated with conditions in which neurons degenerate, lose their function, and often die. Because these diseases are generally progressive, the consequences of neurodegenerative diseases are often very devastating. Patients with neurodegenerative disease may undergo severe deterioration in cognitive or motor skills. As a result, the quality of life and life expectancy of the patients may be considerably reduced. In humans, these diseases include Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), fronto-temporal dementia, cortico basal degeneration, progressive supranuclear palsy (PSP), and other diseases.
Meanwhile, it is known that Nurr1 (nuclear receptor-related 1) protein is implicated in a considerable number of neurodegenerative diseases. The term “Nurr1” refers to nuclear receptor-related 1 protein, also known as NR4A2 (nuclear receptor subfamily 4, group A, member 2). The Nurr1 protein is known to be encoded by the human NR4A2 gene. Although the Nurr1 protein is an orphan nuclear receptor whose ligand has not yet been clearly identified, it was identified that the Nurr1 protein is a member of the nuclear receptor family of intracellular transcription factors, which plays a key role in maintaining the dopaminergic system in the brain. It is known that, when abnormalities in the Nurr1 or NR4A2 gene occur, the function of the dopaminergic system is damaged to cause Parkinson's disease and a wide range of inflammatory and neuropathic diseases, including rheumatoid arthritis, schizophrenia and manic depression.
Parkinson's disease, a typical neurodegenerative disease that is caused by Nurr1 dysfunction, is a chronic progressive neurodegenerative disease that affects brain neurons that control muscle movement. It occurs when cells that produce the neurotransmitter dopamine in substantia nigra are damaged suddenly or degenerated or the number thereof greatly decreases. Because dopamine is an important chemical that is involved in intracellular signaling for facilitating body movement, motor syndromes, including tremor, rigidity, bradykinesia, postural instability and akinesia, typically occur in the case of Parkinson's disease. Although the cause of damage to the dopamine-producing cells has not yet been clearly identified, cerebral arteriosclerosis, carbon monoxide poisoning, it is known that damage to these cells is related to cerebral arteriosclerosis, carbon-monoxide poisoning, medication, metabolic or traumatic encephalitis sequelae induced by hypoparathyroidism, etc.
Known drugs for treating Parkinson's disease include L-dopa drugs, dopamine receptor agonists, anti-cholinergic drugs, Eldepryl (or depreyl), etc. Most of these drugs do not provide causal treatment of Parkinson's disease, but act to control conditions, and thus need to be administered continually. However, the long-term administration of such drugs causes side effects. For example, anti-cholinergic drugs may cause autonomic nervous system abnormalities or abnormal mental functions, and for this reason, continuous administration thereof to aged patients is limited. In addition, in the case of L-dopa drugs, the long-term administration thereof leads to a gradual decrease in the effect and causes side effects, including abnormal movements such as body twisting, or spontaneous movement of the hands or feet.
In order to prevent such side effects, efforts have been actively made to develop natural material-derived agents for treating Parkinson's disease. For example, Korean Patent Laid-Open Publication No. 2001-0081188 discloses a composition for preventing and treating brain diseases and neural diseases, including Parkinson's disease and senile dementia, the composition comprising, as an active ingredient, a Scutellariae radix extract having the effect of protecting neurons. Korean Patent Laid-Open Publication No. 2004-0012396 discloses a composition for treating neurodegenerative diseases such as Parkinson's disease and paralysis, the composition comprising an extract of Beauveria bassiana 101A. Korean Patent Laid-Open Publication No. 2004-0029072 discloses a pharmaceutical composition for treating Parkinson's disease, which comprises an extract obtained from the bark of Wenguanguo. Korean Patent Laid-Open Publication No. 2010-0060123 discloses a pharmaceutical composition for preventing or treating Parkinson's disease, which comprises a ginger extract or shogaol. Korean Patent Laid-Open Publication No. 2010-0060949 discloses a neuron-protecting composition for preventing or treating diseases such as Parkinson's disease, which comprises a peach leaf extract as an active ingredient. Korean Patent Laid-Open Publication No. 2011-0013466 discloses a pharmaceutical composition for treating Parkinson's disease, which comprises, as an active ingredient, a grape seed extract or one or more compounds derived therefrom. These components derived from natural materials have no side effects, but have a shortcoming in that the efficiency of treatment of Parkinson's disease is low.